A regulating transformer with a tap changer is known from U.S. Pat. No. 3,175,148 A. The transformer has a main winding and a regulating winding for each phase. In addition, associated with each phase is a choke (preventive autotransformer) that is used as a switching inductance from the tap changer, which is separately arranged outside at the regulating transformer, during the switching-over processes. The three switching inductances of the three phases are on the upper yoke of the main and regulating windings.
Since the chokes are directly at the yoke, in the case of arrangement of the tap changer on the high-voltage side, thus at the high-voltage potential, these chokes have to be particularly well insulated relative to the transformer yoke at ground potential. This has a significant effect on production costs of chokes of that kind. The connecting of the chokes with the respective tap changers is in that case complicated and similarly has to be very well insulated relative to ground potential.